The purpose of this study is to better define the natural history of primary (acute) HIV infection. Patients who are newly infected with HIV frequently develop an acute mononucleosis-like illness. It has been demonstrated that many of these people have high levels of virus in their blood at the time of this acute illness. Patients will be followed extensively for changes in the immune system and for changes in viral load. Patient recruitment is ongoing, and isolation of lymphocytes for laboratory investigation is performed by the GCRC laboratory.